1. Field of the Invention
This invention relates to a method for producing a multilayer substrate or an electronic part wherein a prepreg or a substrate is used, and also, to an electronic part produced by such method. More specifically, this invention relates to a method for producing a multilayer substrate or an electronic part as well as an electronic part wherein decrease in the layer thickness has been enabled.
2. Description of the Related Art
In the field of electronic equipment for communication, commercial and industrial applications, the current mounting technology seeks further miniaturization and higher density packaging. Concomitant with this trend, materials are required to have better heat resistance, dimensional stability, electrical characteristics and moldability.
Known electronic parts or multilayer substrates for high frequency operation include sintered ferrite and sintered ceramics which are laminated and molded into substrate form. Laminating such materials into multilayer substrates has been practiced in the art because of the advantage of potential miniaturization.
The use of sintered ferrite and sintered ceramics, however, gives rise to several problems. A number of steps are involved in firing and thick film printing. Sintered materials suffer from inherent defects including cracks and warp caused by firing. Cracks are also induced by the differential thermal expansion between sintered material and printed circuit board. It is thus increasingly required to replace the sintered materials by resinous materials.
With resinous materials as such, however, a satisfactory dielectric constant is arrived at with great difficulty, and little improvement in magnetic permeability is achievable. Then, electronic parts utilizing resinous materials as such fail to provide satisfactory characteristics and become large in size, rendering it difficult to reduce the size and thickness of electronic parts.
It is also known from JP-A 10-270255, JP-A 11-192620 and JP-A 8-69712 to mix resinous materials with ceramic powder into composite materials. These composite materials, however, were insufficient in both dielectric constant and magnetic permeability. There was also a problem that increase in the loading of the ceramic powder for the purpose of increasing the dielectric constant was associated with decrease in the strength of the product, and hence, with an increased susceptibility to breakage during the handling and processing.
In addition, these substrates are constituted from a reinforcement such as a glass cloth impregnated with a paste, and thickness of the constituent layer could not be reduced beyond the thickness of the glass cloth. Such substrate also suffered from insufficient reliability and loss of characteristics due to moisture absorption between the glass cloth and the matrix.
Production of a substrate without using a glass cloth is disclosed, for example, in JP-B 6-14600 wherein a sheet of 150 xcexcm is produced by coating and drying of a PET film. This sheet, however, is as thick as 150 xcexcm, and there is no indication for the method of forming the electrode. If the substrate is assumed to have been fabricated by normal method, further reduction in the thickness is difficult.
In view of the rapid progress and widespread use of mobile equipment, decrease in the thickness of the substrate is critical in realizing equipment with reduced thickness and size.
An object of the present invention is to provide a method for producing a multilayer substrate or an electronic part as well as multilayer electronic part wherein decrease in the thickness has been enabled without causing the problem of insufficient strength or the like in the handling.
Such object is attained by the present invention constituted as described below.
(1) A method for producing a multilayer substrate comprising the steps of
adhering a conductor layer to a transfer film,
patterning the conductor layer by etching to form a predetermined pattern,
placing the transfer film overlaid with the patterned conductor layer on a prepreg so that the side of the conductor layer faces the prepreg, and then
adhering the transfer film to the prepreg by applying heat and pressure and peeling the transfer film to produce the prepreg having the conductor layer formed thereon.
(2) The method for producing a multilayer substrate according to the above (1) wherein said adhesion by heat and pressure application is conducted under the conditions including a temperature of 140 to 160xc2x0 C., a pressure of 4.9 to 39 MPa, and a processing time of 120 to 180 minutes.
(3) The method for producing a multilayer substrate according to the above (1) or (2) further comprising the step of heat treating said transfer film at 100 to 130xc2x0 C. for 5 to 20 minutes before placing the transfer film on the prepreg.
(4) The method for producing a multilayer substrate according to any one of the above (1) to (3) wherein the prepreg produced comprises a resin, and at least one of a dielectric powder and a magnetic powder dispersed in the resin, and has a thickness of 2 to 40 xcexcm.
(5) The method for producing a multilayer substrate according to any one of the above (1) to (4) further comprising the step of placing another prepreg on the patterned surface of said prepreg, and adhering the placed prepreg by applying heat and pressure to produce a multilayer substrate having an inner conductor pattern.
(6) The method for producing a multilayer substrate according to any one of the above (1) to (5) wherein said conductor layer has a surface roughness Rz of 1 to 6 xcexcm.
(7) The method for producing a multilayer substrate according to any one of the above (1) to (5) wherein said conductor layer comprises at least one element selected from Cu, Al, Ag, and Au.
(8) The method for producing a multilayer substrate according to any one of the above (1) to (5) wherein said conductor layer is the one formed by electrolysis or rolling.
(9) The method for producing a multilayer substrate according to any one of the above (1) to (5) wherein said conductor layer has a thickness of 3 to 32 xcexcm.
(10) The method for producing a multilayer substrate according to any one of the above (4) to (9) wherein said dielectric powder comprises at least one member selected from titanium-barium-neodymium base ceramics, titanium-barium-tin base ceramics, lead-calcium base ceramics, titanium dioxide base ceramics, barium titanate base ceramics, lead titanate base ceramics, strontium titanate base ceramics, calcium titanate base ceramics, bismuth titanate base ceramics, magnesium titanate base ceramics, CaWO4 base ceramics, Ba(Mg,Nb)O3 base ceramics, Ba(Mg,Ta)O3 base ceramics, Ba(Co,Mg,Nb)O3 base ceramics, and Ba(Co,Mg,Ta)O3 base ceramics.
(11) The method for producing a multilayer substrate according to any one of the above (4) to (9) wherein said dielectric powder comprises at least one member selected from silica, alumina, zirconia, potassium titanate whiskers, calcium titanate whiskers, barium titanate whiskers, zinc oxide whiskers, chopped glass, glass beads, carbon fibers, and magnesium oxide.
(12) The method for producing a multilayer substrate according to any one of the above (4) to (11) wherein said dielectric powder is included at a content in the range of from 10% by volume to less than 65% by volume when the total of the resin and the dielectric powder is 100% by volume.
(13) The method for producing a multilayer substrate according to any one of the above (4) to (12) wherein said magnetic powder comprises at least one member selected from ferrites of Mnxe2x80x94Mgxe2x80x94Zn, Nixe2x80x94Zn, and Mnxe2x80x94Zn base systems.
(14) The method for producing a multilayer substrate according to any one of the above (4) to (12) wherein said magnetic powder comprises at least one member selected from iron carbonyl, iron-silicon base alloys, iron-aluminum-silicon base alloys, iron-nickel base alloys, and amorphous base ferromagnetic metals.
(15) The method for producing a multilayer substrate according to any one of the above (4) to (14) wherein said dielectric powder or said magnetic powder has a spherical shape with a projected image of circle and a sphericity of 0.9 to 1.0, and a mean particle size of 0.1 to 40 xcexcm.
(16) A method for producing electronic parts comprising the steps of
forming electronic part devices by patterning at least the conductor layer of the multilayer substrate of any one of the above (4) to (15),
forming throughholes which function as a terminal for each electronic part device, and
cutting the substrate at the positions of said throughholes into each electronic part device to thereby produce the electronic parts.
(17) A multilayer electronic part produced by the production method of the above (16).
(18) A multilayer electronic part wherein
said multilayer electronic part comprises constituent layers which comprise at least one of a dielectric material and a magnetic material dispersed in a resin, and which include no glass cloth, and
said constituent layer including no glass cloth has a thickness of 2 to 40 xcexcm.